Introduction
Cropping an Image is pretty simple in VB.Net.
Today I had a need to make it possible for my users to crop some images by drawing a selection rectangle and I felt the need to reinvent the wheel ;-).
Not zoomed image
Cropping isn’t all that difficult with VB. As you can see from the following piece of code.
Dim bmp As New Bitmap(newwidth,newheight)
Dim g = Graphics.FromImage(bmp)
g.DrawImage(PictureBox1.Image,0,0, New Rectangle(newtop, newleft, newwidth, newheight), GraphicsUnit.Pixel)```<div class="image_block">
<a href="/wp-content/uploads/users/chrissie1/croppedimage/CroppedImage1.png?mtime=1294047503"><img alt="" src="/wp-content/uploads/users/chrissie1/croppedimage/CroppedImage1.png?mtime=1294047503" width="860" height="556" /></a>
</div>
First thing to do was show the image, since these are scanned pages from books they are going to be a rather large format. So the picturebox will have to be able to zoom to show the image. Now this is where it gets interesting. But I did ;-). The biggest problem was to detemine the zoomfactor used in the original so that the cutout would match. Perhaps I’m doing it all wrong but it works.
<div class="image_block">
<a href="/wp-content/uploads/users/chrissie1/croppedimage/CroppedImage.png?mtime=1294047492"><img alt="" src="/wp-content/uploads/users/chrissie1/croppedimage/CroppedImage.png?mtime=1294047492" width="860" height="556" /></a>
</div>
And here is the not yet perfect code.
```vb.net
Imports System.Drawing.Drawing2D
Public Partial Class MainForm
Private _CropRectangle As CropRectangle
Private _ZoomFactor As Double
Public Sub New()
Me.InitializeComponent()
_CropRectangle = New CropRectangle
If pictureBox1.Image.Width > pictureBox1.Image.Height Then
_ZoomFactor = Me.Panel1.Width / pictureBox1.Image.Width * 100
Else
_ZoomFactor = Me.Panel1.Height / pictureBox1.Image.Height * 100
End If
If (pictureBox1.Image.Height / 100 * _ZoomFactor) > (Me.Panel1.Height) Then
_ZoomFactor = (Me.Panel1.Height) / pictureBox1.Image.Height * 100
End If
If (pictureBox1.Image.Width / 100 * _ZoomFactor) > Me.Panel1.Width Then
_ZoomFactor = Me.Panel1.Width / pictureBox1.Image.Width * 100
End If
If _ZoomFactor < 0.2 Then
_ZoomFactor = 0.2
End If
If _ZoomFactor > 100 Then
_ZoomFactor = 100
End If
Dim _Height As Integer
_Height = Convert.ToInt32 (Me.PictureBox1.image.Height/100*_ZoomFactor)
Dim _Width As Integer
_Width = Convert.ToInt32 (Me.PictureBox1.image.Width/100*_ZoomFactor)
Dim _Left As Integer
If _Width < Me.Panel1.Width Then
_Left = Convert.ToInt32 ((Me.Panel1.Width - _Width)/2)
Else
_Left = 0
End If
Dim _Top As Integer
If _Height < (Me.Panel1.Height) Then
_Top = Convert.ToInt32 ((Me.Panel1.Height - _Height)/2)
Else
_Top = 0
End If
_CropRectangle.ZoomFactor = _ZoomFactor
setImage(True, _Height, _Width, _Left, _Top)
End Sub
private Sub SetImage(ByVal Visible As Boolean, ByVal Height As Integer, ByVal Width As Integer, ByVal Left As Integer, ByVal Top As Integer)
PictureBox1.Visible = Visible
PictureBox1.Height = Height
PictureBox1.Width = Width
PictureBox1.Left = Left
PictureBox1.Top = Top
End Sub
Private Sub PictureBox1_MouseDown( ByVal sender As System.Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles PictureBox1.MouseDown
_CropRectangle.CropX = e.X
_CropRectangle.CropY = e.Y
_CropRectangle.CropX2 = e.X
_CropRectangle.CropY2 = e.Y
_CropRectangle.Initialized = True
End Sub
Private Sub PictureBox1_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles PictureBox1.MouseMove
If _CropRectangle.Initialized = True
_CropRectangle.CropX2 = e.X
_CropRectangle.CropY2 = e.Y
_CropRectangle.Draw(Me.PictureBox1)
end if
End Sub
Private Sub PictureBox1_MouseUp(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles PictureBox1.MouseUp
_CropRectangle.Initialized = False
_CropRectangle.DrawCroppedImage(PictureBox1, PictureBox2)
End Sub
Private Class CropRectangle
Private _CropPen As Pen
Public Sub New
_cropPen = New Pen(Color.green, 1)
_cropPen.DashStyle = DashStyle.Dot
End Sub
Public Property Initialized As Boolean = False
Public Property CropX As Integer
Public Property CropY As Integer
Public Property CropX2 As Integer
Public Property CropY2 As Integer
Public Property ZoomFactor As Double
Public readonly Property CropPen As Pen
Get
Return _CropPen
End Get
End Property
Public sub DrawCroppedImage(ByVal PictureBox1 As PictureBox, Byref PictureBox2 As PictureBox)
Dim bmp As New Bitmap(Convert.ToInt32((_CropX2 - _CropX)/ZoomFactor*100), Convert.ToInt32((_CropY2 - _CropY)/ZoomFactor*100))
Dim g = Graphics.FromImage(bmp)
g.DrawImage(PictureBox1.Image,0,0, New Rectangle(_cropx/ZoomFactor*100, _cropy/ZoomFactor*100, (_cropx2 -_cropx)/ZoomFactor*100, (CropY2 - _cropy)/ZoomFactor*100), GraphicsUnit.Pixel)
PictureBox2.Image = bmp
End Sub
Public sub Draw(ByRef PictureBox1 As PictureBox)
PictureBox1.Refresh()
Dim g = PictureBox1.CreateGraphics
g.DrawRectangle(_cropPen,_cropx, _cropy, _cropx2 -_cropx, CropY2 - _cropy)
End Sub
End Class
End Class
Here is the downloadable code in VS 2010 format.
Chris is awesome.
